Force measuring wheel for vehicles

ABSTRACT

A measuring wheel detects forces and moments between the rim and axle of a vehicle wheel with measuring sensors between the rim face and a wheel flange apparatus transmits the energy and data to a measurement evaluation and processing system on the vehicle. The wheel flange and/or the front of the rim consists of a fiber compound, while the apparatus on the wheel for transmitting energy and data are fitted on the inside of the rim bed holding the vehicle tire and extends essentially over its circumference. Thus the static properties and dynamic behavior of the measuring wheel during travel correspond to the greatest degree to the original wheel. Effects which falsify the measurements such as increased wheel weight and the like do not arise.

The invention relates to a measuring wheel for detection of forces andmoments between the rim and axle of a vehicle tire.

Operational stability tests and studies of vehicle movement dynamicsrepresent essential elements in the development of vehicles, inparticular in connection with safety-relevant functional groups, whichinclude vehicle wheels and the chassis in which they are housed.

The studies in question are conducted on load test stands and in avehicle. The prerequisite is that the forces occurring during driving bedetermined in a driving test.

Measuring wheels are employed for such a multicomponent powermeasurement at a rotating wheel. The power flux is guided throughsuitable measuring elements at an interface in the measuring wheel.Spring elements with measuring extension strips (DMS) or quartz sensorsare commonly used for this purpose. The test values obtained areconverted online or offline from the rotating coordinate system of thewheel to the coordinate system of the vehicle. It is also necessary forthis purpose to determine the angular position of the wheel.

Exemplary embodiments of such measuring wheels and test executiondetails are presented, for example, in the report entitled"Multicomponent measuring hubs, potential applications, and results" andpublished in ATZ Automobiltechnische Zeitschrift 94 (1992), pages 44 to53. The multicomponent wheel hub shown in detail as an example on page45 consists of a modified rim, a wheel flange, a measuring sensor, andan electronic component. The measuring sensor performs the function ofsensing dynamic forces and moments. The DMS applications necessary fordetermining these forces are executed on a specially designed aluminumcomponent. The electronic component includes a constant-voltageamplifier for each measured quantity, a slip ring rotation transducer,and a resolver for determination of the wheel position (angle ofrotation of the wheel about the Y axis).

A measuring wheel such as this presents the major disadvantage thatneither statically nor dynamically does it correspond to an originalwheel subsequently installed on the vehicle. The design of the testequipment considerably increases the weight of the wheel, and also thecomponents projecting a relatively great distance forward (slip ringrotation transducer, resolver) exert an additional effect of momentduring driving and create a hazard in public road traffic; theseconsiderations make measurement during operation by customers impossibleor at least extremely difficult. And so a description is given on page46, Section 2.2, of this reference of the attempt made to compensate forthese factors which distort the results.

While a modified multicomponent wheel measurement hub is described onpage 53 in FIG. 24 (where the resolver is replaced by an incrementaltransmitter, the slip ring rotation transmitter by an infrared telemetrystrip, and the power supply of the electronic component is inductive),one in which the total width of the measuring system was reduced, onlyto a certain extent have the disadvantages discussed above beeneliminated.

In the light of what has been stated the object of the invention is todevelop the state-of-the-art measuring wheel so that this wheel willcorrespond to the original wheel to the greatest extent possible withrespect to its static properties and its dynamic behavior.

DE 39 37 966 A1 discloses the mounting of a part of a measurement signaltransmitter on the inside of a wheel rim in order to correspond with asignal receiver on the body side by way of the pertinent transmitter,signal transmission being accomplished free of contact, as for exampleby inductance with a frequency-modulated signal or by way of slip rings.Of course, this prepublication describes not a measuring wheel butrather a process and a device for determination of the closed linkagerelationships between vehicle tire and roadway, for which purpose atleast one sensor is mounted in the tire tread to detect the patterns oflocal voltages, expansions, or strains in the horizontal and verticaldirections. Both the current closed linkage coefficient and the maximumpossible closed linkage coefficient between the vehicle tire and theroadway can thus be determined.

A preferred development is described in what follows. In theaccompanying drawings,

FIG. 1 shows a wheel of a motor vehicle, together with the forces andmoments arising during driving,

FIG. 2 a diagram of the cross-section of the measuring wheel claimed forthe invention along arrow II in FIG. 4,

FIG. 3 a side view of the associated stator fastened on the wheel axis(shock strut), and

FIG. 4 a view of the measuring wheel along arrow IV in FIG. 2.

Forces F_(X), F_(Y), F_(Z) acting in the directions indicated by arrowsand moments M_(X), M_(Y), and M_(Z) acting around the X-, Y-, and Z-axes as shown in Figure occur on each wheel 1 during driving.

The measuring wheel 2 illustrated in FIGS. 2 and 4 performs the functionof determining these three external forces and moments referred to thewheel contact point. A tire 3, represented by broken lines, is mountedby a state-of-the-art method in a well 4 consisting, for example, of analuminum alloy, of a rim 5. A face of the rim 8 connected to the rimwell 4 and joined to a wheel flange 7 by way of transducer (DMS forcetransducers 6) consists, as does the cupshaped wheel flange 7 formed inthe central inner part, of a fiber reinforced material (CFK=carbon fiberreinforced plastic). If desired, it might be sufficient, for the desiredreduction of the weight of the measuring wheel 2, for the sake ofoptimizing the static and dynamic properties, to produce only one of thetwo components (wheel flange 7, rim face 8) of a fiber reinforcedmaterial and the other, as is customary, of metal.

The connection between rim well 4 and rim face 8 is made by producingthe fiber reinforced material in the previously sand blasted rim well 4.The connection thus has the effect of a large-area glued joint (adhesionforces). In addition, the rim well is worked prior to the sand blasting(ribs 9) so that a positive connection is established which secures theconnected parts against axial and radial displacements. Lastly, the agehardening of the rim face 8 is controlled so that the rim well 4 issubjected to tensile prestressing. Since the fiber reinforced materialCFK employed has a high E modulus (approximately 100,000 N/mm²), the rim5 as a whole possesses a rigidity corresponding to that of amass-produced rim.

The wheel flange 7 is connected by screws 13 seated on titanium bases 10to the wheel axle not shown here. An additional inserted washer 14, forexample, one of a polyimide or ceramic material, provides a certainamount of thermal insulation from heat passing into the measurementsystem to be explained below, for example, during braking processes.

If the wheel flange 7 is in the square form shown in FIG. 4, withlateral edges curving inward, openings 22 made in these areas in the rimface 8 can effect additional heat removal outward.

Four DMS force transducers 6 are spaced evenly over the circumference astransducers, between rim face 8 and wheel flange 7, inside a cavity 16formed by the outline (central cup 11, bevelled edge 15) of the wheelflange 7, and are connected to the wheel flange 7 or the rim face 8 bymeans of screw connections 17. Depending on the size of the measuringwheel 2, a larger number of force transducers 6 may, of course, beemployed, but there must be a minimum of three. As a result of thestructure of the transducers, both static and dynamic test signals canbe detected accurately. Consequently, both the individual integratedanalyzers and the measuring wheel 2 as a whole can be staticallycalibrated with high accuracy. Each of the four DMS force transducers isof state-of-the-art design and generates three signals corresponding tothe forces arising in it, F_(X), F_(Y), and F_(Z). Initial signalprocessing can be accomplished in the force transducer 6 itself byelectronic boards installed in them, ones which among other thingsperform the function of signal preamplification and crosstalkcompensation. The signals reaching an electronic unit 18 introduced intothe central cup 11 over cables 19 from the force transducers 6 areconsequently already preamplified to the extent that the influence ofnoise fields from the electronic equipment of the vehicle is eliminated.

Other noise signals could be generated by additional stresses on theforce transducers 6 distorting the measured values, ones caused bytemperature rises due to repeated braking and the resulting thermalexpansion of wheel flange 7 and rim face 8. In this respect as well thematerial selected naturally exerts a highly positive effect for wheelflange 7 and rim face 8, since the fiber reinforced material CFK ischaracterized by very low thermal expansion (significantly lower thanthat of steel or aluminum).

The twelve force signals (from four force transducers 6 each generatingthree force signals F_(X), F_(Y), and F_(Z)) move, by way of a jackmount 20 extending into the central cup 11 of the wheel flange 7 andfastened on the wheel flange 7 by means of screws 21 (see FIG. 4), intothe electronic unit 18 held by the jack mount 20 (screw connections 23),the electronic unit 18 being mounted on the jacks provided for thispurpose in the jack mount 20.

The total forces and total moments are made up of the individual forcesby a state-of-the-art process in the electronic unit 18. These signalsare digitized along with a signal from a temperature sensor which shouldbe mounted in an area of the measuring wheel 2 subjected to thermalloads, for example, by braking processes, and a voltage monitoringsignal. These data are converted to a serial PCM (pulse code modulation)data stream and sent after frequency modulation over cables 24 to a coiland magnet ring 25 of glass fiber reinforced plastic cemented on theinside of the rim well 4. The coil and magnet ring 25 serves asreceptacle for integrated data transmission and energy reception coils26, 27, and in addition has, on its inner side 29 facing a stator 28mounted on the side of the vehicle, a magnetic track consisting offerrite magnets 30 mounted at uniform intervals over the circumferenceand of timing magnets 31.

It is expedient to face the coil and magnet ring 25 on its side facingthe rim well 4 with several layers of magnetically conducting foil inorder to shield the magnetic fields of the coils 26, 27 from the rimwell 4.

Associated with the coil and magnet ring 25 is the stator 28 alreadyreferred to, which is mounted on the body side (on a shock strut, forexample). This stator 28 supports the components corresponding to thedata transmission coil 26, energy reception coil 27, and the magnetictrack (ferrite magnets 30, timing magnets 31). The stator housing itselfis also made of a glass fiber reinforced plastic and consists of a baseelement 33 which is adapted to the rim well profile, that is, its shapeis that of a round arch, and is surmounted by a cover 34. A receptioncoil 35 for data transmission, an electronic board 36 with integratedHall sensors (four angle sensors 37 mounted in series at equal intervalsand an adjacent timing sensor 41 for zero marking and recognition of thedirection of wheel rotation), and a transmission coil 38 with coil core39 are fastened in succession on the base element 33 for energytransmission to the electronic unit 18. These units are connected by acommon data/energy cable 40 to the test value acquisition and processingsystem on the vehicle side.

An open conducting loop may be employed as an alternative in the coiland magnet ring 25 in place of the data transmission coil 26 on thewheel side. In this instance the reception coil 35 would be replaced bya miniature spool and a preamplifier in the stator 28.

Energy is transmitted over inductively coupled resonance circuits, theoperating frequency being around 50 kHz. The distance between stator 28and coil and magnet ring 25 may range from 0 to 5 mm. transmission coil38 and energy reception coil 27 should have taps for adaptation of agenerator or power consuming device. Data are also transmitted overinductively coupled resonance circuits; the magnetic fields in energyand data transmission may be oriented in different directions in space.This can be accomplished by means of a symmetrical winding structure forthe transmission coil 38 and energy reception coil 27 in energytransmission and winding in the opposite direction for the transmissioncoil 38 and energy reception coil 27 in data transmission. There isconsequently little input of energy transmission into data transmission.

The four angle sensors 37 are mounted in an arc spaced at angles of 2.5°in the base element 33 of the stator. They detect the field of 180ferrite magnets 30 cemented at intervals of 2° on the magnetic track.This yields a wheel rotation angle resolution of 0.5°, since an anglesensor 37 is aligned with a ferrite magnet 30 after every 0.5° ofrotation. The timing sensor 41 recognizes three timing magnets 31mounted beside the ferrite magnets 30. The sensor signals are evaluatedin an electronic angle measurement unit which is part of the test valueacquisition and processing system on the vehicle side. In this unit acounter counts incrementally upward and downward, depending on thedirection of travel.

As a result of application of the measuring wheel 2 claimed for theinvention, an energy and data transmission system projecting beyond thelateral profile of a vehicle and the support frame such a systemrequires may be dispensed with.

Hence no road traffic hazard is created.

We claim:
 1. A vehicle measuring wheel for detection of forces andmoments between a rim of said vehicle measuring wheel and a vehicularaxles, said vehicle wheel comprising:a plurality of force transducersfor generating energy and data signals mounted between a rim face and awheel flange of said vehicle measuring wheel; signal coupling meanscoupled to said vehicle wheel and said plurality of force transducersfor transmitting and receiving said energy and data signals; and a testvalue acquisition and processing system for transmitting and receivingtest values and said energy and data signals and for processing saidtest values and said energy and data signals, said system being disposedwithin a vehicle upon which said vehicle measuring wheel is coupled andcoupled to said vehicle measuring wheel, wherein at least one of saidwheel flange and said rim face comprises a fiber reinforced material andsaid signal coupling means is mounted along the circumference of a rimwell disposed within said measuring wheel.
 2. A vehicle measuring wheelas claimed in claim 1, wherein said rim face is fitted upon a pluralityof connection points disposed upon said measuring wheel by means ofribs, said ribs securing said rim face against axial and radialdisplacements.
 3. A vehicle measuring wheel as claimed in claim 1,wherein said wheel flange further comprises:a bevelled edge; and acentral cup wherein said bevelled edge forms, in cooperation with saidrim face a plurality of cavities for receiving said plurality of forcetransducers, said plurality of force transducers for measuring relativeforces between said wheel flange and said rim face, said central cup forreceiving an electronic unit.
 4. A vehicle measuring wheel as claimed inclaim 3, wherein said wheel flange is of a modified square shape, withinward curving openings made upon the sides of said modified squareshape, said inward curving openings coinciding with open areas in saidrim face for effecting heat removal outward from inside said vehiclemeasuring wheel.
 5. A vehicle measuring wheel as claimed in claim 3,wherein said wheel flange is further connected to said vehicular axle byscrew connections located in a bottom face of said central cup andfurther comprises a thermal insulating washer inserted between saidvehicular axle and said bottom face of said central cup.
 6. A vehiclemeasuring wheel as claimed in claim 3, wherein said plurality of forcetransducers further comprises four force transducers distributed evenlyover the circumference of said measuring wheel and disposed within saidplurality of cavities, said force transducers being connected to saidwheel flange and said rim face by means of screw connections.
 7. Avehicle measuring wheel as claimed in claim 6, wherein said forcetransducers are coupled to said electronic unit by means of a firstcable assembly, said force transducers for generating orthogonal forcesignals in the x, y, and z directions and communicating said forcesignals to said electronic unit by means of said first cable assembly.8. A vehicle measuring wheel as claimed in claim 1, said signal couplingmeans further comprises a coil and magnet ring cemented on the innerside of a rim well said coil and magnet ring extending over thecircumference of said rim well, said coil and magnet ring furthercomprising a plurality of data transmission coils and a plurality ofenergy reception coils and a magnetic track for determining the angularposition and zero marking of rotation of said vehicle measuring wheel.9. A vehicle measuring wheel as claimed in claim 8, wherein said coiland magnet ring further comprises a plurality of layers of magneticallyconducting foil disposed between said rim well and said coil and magnetring for shielding said rim well from magnetic fields emanating fromsaid plurality of data transmission coils and said plurality of energyreception coils.
 10. A vehicle measuring wheel as claimed in claim 8,wherein said vehicular axle further comprises a stator disposed inproximity to said coil and magnet ring comprising a first complimentaryelement coupled to said stator for communicating with said plurality ofdata transmission coils, a second complimentary element coupled to saidstator for communicating with said plurality of energy reception coils,and a third complimentary element coupled to said stator forcommunicating with said magnetic track said stator connected to saidtest value acquisition and processing system by means of a second cableassembly.
 11. A vehicle measuring wheel as claimed in claim 10, whereinsaid first complimentary element further comprises a reception coilcoupled to said stator for communicating data between said stator andsaid coil and magnet ring, said second complimentary element furthercomprises a transmission coil for communicating energy to saidelectronic unit between said stator and said coil and magnet ring, andsaid third complimentary element further comprises Hall effect sensorscoupled to said stator for sensing moving magnetic fields correspondingto rotation of said coil and magnet ring.
 12. A vehicle measuring wheelas claimed in claim 11, wherein said first complimentary elementcomprises a first wound coil and said second complimentary elementcomprises a second wound coil, wherein said first and second coils arewound in opposite directions, and said plurality of data transmissioncoils and said plurality of energy reception coils comprise windingswound in opposite directions such that the resulting magnetic fields forenergy and data transmission respectively are oriented in differentdirections in space.
 13. A vehicle measuring wheel as claimed in claim11, wherein said third complimentary element further comprises fourangle sensors mounted in an arc at intervals of 2.5° on said stator,said angle sensors for communicating with said magnet track, said magnettrack further comprising 180 ferrite magnets cemented to said coil andmagnet ring at intervals of 2°.
 14. A vehicle measuring wheel as claimedin claim 1 wherein at least one of said wheel flange and rim facefurther comprise and said coil and magnet ring further comprises.